Regardless of what font size you use, many people are arrested for crimes they didn't commit. That's just the way the system works.

The cop doesn't need to read your rights unless he's interrogating you while you're in custody. If that was the case, you can get any confessions you might have made thrown out of court.

Keep in mind that concealing merchandise is considered intent to steal and you can be arrested for larceny for doing such a thing. However, the fact that you actually walked out of the store with no unpaid merchandise could let you beat the charge; if concealing is intent to steal, then refraining from stealing and leaving without any unpaid merchandise shows intent not to steal.

In the future, you should avoid eagerly confessing to the police or store personnel. Anything you say can be used against you in court— even if it's not technically incriminating.